Huanglong is a staircase of golden stone 3.6 kilometres long, set with hundreds of pools and running down an alpine valley in northern Sichuan, China, and not one of those colours belongs to the water. The floor of every basin is travertine, pale lime dropped out of the spring water, and it throws sunlight straight back up at you. Shallow pools send back gold and amber, deeper ones scatter blue and green, and mineral films tint the edges. The same water reads a different colour in each basin it falls into. That lime builds the rims as well. The spring water arrives carrying dissolved limestone, loses its carbon dioxide to the air and leaves calcite along every lip, a few millimetres a year. Huanglong means yellow dragon, and in the legend one helped Yu the Great channel China's floods and then settled here, its scaled body becoming these terraces. A Ming-era Taoist temple still stands for it at the head of the valley.
The boardwalk switchbacks up through pine and larch, and every bend you turn opens onto a fresh run of colour. It is only a few kilometres, but the valley tops out near 3,600 metres and the thin air makes it far longer on your lungs than the distance suggests. A cable car up one side carries most people to the top to walk down instead. Coming back down is the quiet half, winding among pools half hidden in the forest where the only sound is water slipping from one rim into the next. Somewhere above, in old-growth forest nobody walks into, are giant pandas and golden snub-nosed monkeys. From late September to mid-October the larch and maple above the terraces turn gold and crimson, and a single cold snap can strip them within days. At the head of the valley a platform puts you above the Five-Colour Pond, several hundred basins running jade into amber into ice-blue, all of it the same water over the same white stone at different depths.